Two‐Stage Agricultural Ditch Sediments Act as Phosphorus Sinks in West Michigan

Abstract

Phosphorus (P) and sediment inputs from agricultural drainage contribute to the development of hypereutrophic conditions in lakes across the world. Two‐stage (2‐S) ditches, an agricultural best management practice gaining acceptance in the Midwestern United States, increase floodplain area within drainage ditches to help capture nutrients and sediment. While denitrification has been shown to increase on 2‐S benches, less is known about their P retention ability. This study assessed the abiotic and biotic P retention of two separate 2‐S ditches compared to their corresponding traditional reaches directly upstream within the Macatawa watershed, located in West Michigan. Soluble reactive P export was significantly reduced in 2‐S baseflow of both ditch systems. Equilibrium P concentration values suggest retention of P within the 2‐S sediment. P was bound within stable fractions in both 2‐S and traditional reaches. An analysis of P stock within the ditches revealed sediment held over 96% of total P (TP) within each reach compared to <4% in bench vegetation and periphyton combined. Turbidity, but not TP, was reduced in one study ditch, whereas TP, but not turbidity, was reduced in the other study ditch. Geomorphic stability may have been responsible for differing P retention between ditches. Ability to retain P appears to be impacted by physical as well as biogeochemical characteristics; hence, structure and age of 2‐S reaches influence P retention.

Phosphorus supply and floodplain design govern phosphorus reduction capacity in remediated agricultural streams

“…The range of TP content in channel bed sediments was consistent with other agricultural streams in Sweden (0.07-1.57 g P kg −1 , Lannergård et al, 2020; 0.35-1.85 g P kg −1 , Sandström et al, 2021), indicating that remediated streams do not promote P enrichment in channel beds compared with streams without floodplains. However, the proportions of labile P fractions were overall lower in our study, either explained by less deposition of these fractions or a more rapid turnover of labile P. In a comparable system, sediments were also dominated by recalcitrant fractions that were shown to be stable over seasons (Kindervater and Steinman, 2019). The increase in Al-P with construction age was partly explained by higher clay content in catchment soils, which often are rich in Al silicates and hydroxides that increase the sorption of P to these surfaces (Gérard, 2016).…”

“…Although soil organic carbon has been found to accumulate more over time in floodplain sediments than in channel sediments (Hallberg et al, 2022;Speir et al, 2020), the lack of increase in organic P in floodplain sediments with construction age suggests that the build-up of organic P forms, despite the presence of vegetation, is slow and requires more than 10 years to occur. In this study, P in vegetation biomass was not considered and although it could contribute as a seasonally active P sink, Kindervater and Steinman (2019) reported that channel and floodplain sediments on average held 18 times more P mass than biomass on a reach-scale.…”

Influence of vegetation maintenance on flow and mixing: case study comparing full cut with high-coverage conditions

“…While environmentally friendlier vegetation maintenance practices and channel designs have been proposed in the past (Buisson, 2008;SEPA, 2009), traditional ecologically harmful cutting and dredging practices continue to be applied, despite their large-scale negative influences on agricultural streams and rivers (Old et al, 2014;B ączyk et al, 2018). On the other hand, in two-stage channels and other nature-based designs, clever, environmentally friendlier vegetation maintenance may provide possibilities for enhancing the retention of suspended sediment and nutrients while maintaining flow conveyance (e.g., Kindervater and Steinman, 2019;Västilä et al, 2021). However, optimising the performance of such vegetated channel designs requires an improved understanding of the influence of spatially variable vegetation distributions on transport and mixing processes (e.g., Rowiński et al, 2021).…”